1. Field of the Invention
The present invention relates to a storage battery system using a secondary battery.
2. Description of Related Art
Performance and life time of a secondary battery strongly depend on the temperature of the secondary battery. Since the likelihood of deterioration increases at high temperatures, with a secondary battery system that requires a large current such as that of a hybrid vehicle, a cooling performance of a cooling system during charge and discharge must be accurately monitored. Cooling methods of secondary batteries can be divided into two methods, namely, an air-cooling method in which air is supplied by a fan to cool a secondary battery and a liquid-cooling method in which a liquid cooling medium is circulated to a secondary battery to transfer heat to the outside. Conceivable causes of degradation of a cooling performance in an air-cooling method include fan failure and accumulation of dust and extraneous matter on the secondary battery or in a draft air duct. Conceivable causes of degradation of a cooling performance in a liquid-cooling method include a failure of a pump that circulates a cooling medium, a change in components of the cooling medium, and deterioration due to metal corrosion in a cooling medium flow channel. As a technique for judging an abnormality in the cooling performance of such a secondary battery cooling system, Japanese Patent Laid-Open No. 2001-313092 discloses a storage battery system configured so as to estimate a temperature of a secondary battery from a charge and discharge current and a cooling state of the secondary battery, and to judge an abnormality in cooling performance by comparing the estimated temperature with a measured temperature of the secondary battery.